Bi-level heat sink

ABSTRACT

A bi-level assembly comprises a heat sink, a processor and a power supply. The heat sink includes a base and at least one fin structure attached to the base. The base may be a plate with attached heat pipes or the base may be a vapor chamber. The base is connected to the top of the processor and power supply and has an s-bend to accommodate the differing heights of the processor and power supply. Heat from the higher heat generating processor may be transferred by the base and dissipated by the fins above the power supply.

FIELD OF THE INVENTION

The present invention relates generally to heat sinks and, moreparticularly, to heat sinks using heat pipe technology to efficientlyutilize space in computer applications.

DESCRIPTION OF THE RELATED ART

The performance of electronic circuits and their semiconductor devicesis affected by temperature and temperature swings. Semiconductor deviceperformance degrades when the internal temperature reaches or exceeds aparticular limit. For example, in silicon integrated circuit devices,for each ten degree centigrade rise in junction temperature, theoperating lifetime of the semiconductor device is decreased by a factorof at least two. Demands by original equipment manufacturers (OEMs) forsmaller package sizes and increased device densities has resulted inhigher power densities and corresponding increases in temperature, withthe concomitant need for efficient heat dissipation becoming extremelyimportant.

The current trend in microprocessor design is to increase the level ofintegration and to shrink processor size. This results in an increase inboth the raw power as well as the power density on silicon.Correspondingly, there is a desire to manage yield and reliability, allresulting in a need for lower operating temperatures. Compounding thethermal challenge is a thirst for a smaller form-factor chassis. Inorder to meet the demand for smaller, faster processing systems whilestill maintaining adequate cooling, it is critical to efficiently managethe thermal design space at the system level.

The newest workstations and servers are using 64-bit microprocessorswhich can generate more than 100 watts of heat. System reliabilitydepends on keeping these microprocessors cool. Typically, workstationsand servers using these microprocessors use expensive, custom-engineeredheat sinks and large, variable-speed fans for cooling. Often the heatsink is located directly above the microprocessor, or a heat pipe isused to transfer heat from the microprocessor to a heat sink.

Certain designs for “ITANIUM™” processor based systems include “ITANIUM™” 64-bit microprocessors (by Intel Corporation of Santa Clara, Calif.)having power bricks sitting beside them. A heat sink is attached to thetop of the microprocessor. As rack space in these systems is extremelyexpensive, platform designers want to make the best use of spacepossible. Currently, valuable space above the power supply is not beingutilized. An, improved, more efficient heat transfer system is desired.

SUMMARY OF THE INVENTION

The present invention is an assembly comprising a processor having afirst height. A component is next to the processor. The component is aheat source. The component has a second height different from the firstheight. A heat sink includes a base and at least one fin structure. Thebase of the heat sink is continuous and has a first side abutting thecomponent and the processor. The base has an offset between theprocessor and component. The at least one fin structure is attached to asecond side of the base opposite the first side.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention is morefully disclosed in the following detailed description of the preferredembodiments of the invention, which are to be considered together withthe accompanying drawings wherein like numbers refer to like parts andfurther wherein:

FIG. 1 is an isometric view of a processor/power supply/bi-level heatsink assembly having embedded heat pipes formed in accordance with oneembodiment of the present invention;

FIG. 2 is a top plan view of the bi-level heat sink shown in FIG. 1;

FIG. 3A is a cross-sectional view of the bi-level heat sink shown inFIG. 1;

FIG. 3B is a cross-sectional view of a variation of the bi-level heatsink shown in FIG. 3A;

FIG. 4 is a bottom view of the bi-level heat sink shown in FIG. 1;

FIG. 5 is a side view of a heat pipe to be embedded in the base of thebi-level heat sink of FIG. 1.

FIG. 6 is a top view of a bi-level heat sink having bi-level vaporchamber formed in accordance with another embodiment of the presentinvention; and

FIG. 7 is a cross-sectional view of the bi-level heat sink shown in FIG.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This description of the preferred embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description of this invention. In thedescription, relative terms such as “lower,” “upper,” “horizontal,”“vertical,”, “up,” “down,” “top” and “bottom” as well as derivativethereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing figure under discussion. These relative terms are forconvenience of description and normally are not intended to require aparticular orientation. Terms concerning attachments, coupling and thelike, such as “connected” and “interconnected,” refer to a relationshipwherein structures are secured or attached to one another eitherdirectly or indirectly through intervening structures, as well as bothmovable or rigid attachments or relationships, unless expresslydescribed otherwise.

Referring to FIG. 1, an assembly 11 formed in accordance with oneembodiment of the present invention includes a processor 10, a component20 (which may be a power supply), and a bi-level heat sink 30. Theprocessor 10 and power supply 20 are preferably in side-by-siderelation, next to one another and have different heights from eachother, where the heights are measured from the circuit board 12 on whichprocessor 10 and power supply 20 are mounted. The processor 10 mayinclude any type of integrated circuit package, but is preferably amicroprocessor or CPU for computer applications. A preferred applicationfor use of assembly 11 is on the motherboard of a workstation or serveremploying the Intel “ITANIUM ™” 64-bit processor, wherein one currentdesign includes the processor and the power supply situated beside eachother on the board.

Referring to FIGS. 2-4, the bi-level heat sink 30 formed in accordancewith one exemplary embodiment of the present invention includes a base32, processor fins 34 and power supply fins 36.

Processor fins 34 and power supply fins 36 are preferably folded finsformed from a single sheet of metal, such as aluminum or copper.Although shown in FIGS. 1 and 3 as two separate folded fins,alternatively, processor fins 34 and power supply fins 36 may be formedfrom a single sheet of metal. By folding the fins over themselves, thefolded fin assembly provides a large surface area in a small space witha low weight. Folded fin technology maximizes surface area and minimizespressure drop, thus increasing the flow of heat from the heat generatingsource to the air. Preferably, the folded fin has an open top design toallow for natural convection, in addition to forced convection. Otheralternative types of fin structures may also be employed includingextruded, stamped, cold forged or machined fins, pin fins, bonded fins,or the like.

Referring again to FIGS. 1-4, base 32 includes a plate 40, channels 42and embedded heat pipes 44. Plate 40 is comprised of a solid conductivemetal, which is preferably aluminum or copper. Plate 40 includes a lowerlevel 50, an upper level 52 and a connecting section 54 between thelower and upper levels, which may be referred to as an offset, a bentsection, or a dog-leg 54. Plate 40 has an opening 46 in the offset 54 toprovide clearance for bends in heat pipes 44, since the heat pipestypically don't include a zero-radius or mitered joint. Lower level 50of plate 40 is mechanically and conductively coupled to processor 10.Upper level 52 is mechanically and conductively coupled to power supply20. Offset 54 connects lower level 50 and upper level 52.

The base 40 has a lower condenser section 51 and an upper condensersection 53, and the at least one fin structure includes a first finstructure 34 attached to the lower condenser section 51 and a second finstructure 36 attached to the upper condenser section 53. The base 40 hasa lower evaporator section 55 located on top of the processor 10 and theupper evaporator section 56 located on top of the component 20.

The height difference between lower level 50 and upper level 52 of plate40 depends on the differing heights of the processor 10 and power supply20.

In the exemplary embodiment of FIGS. 1-3A, the first and second finstructures 34, 36 have different heights H1 and H2, respectively, fromeach other. The first fin structure 34 is above the processor 10. Thesecond fin structure 36 is above the component (power supply) 20. In theembodiment of FIGS. 1-3A, the first fin structure 34 has a greaterheight H1 (measured from the bottom of the fin structure to the top ofthe fin structure) than the height H2 of the second fin structure 36. Asbest seen in FIG. 3A, the top of fin structures 34 and 36 are at thesame height H3 (measured from the printed circuit board 12 beneathprocessor 10 and power supply 20, so that the tops 34 t, 36 t of the finstructures 34 and 36 are parallel. Having the tops 34 t and 36 tparallel allows the maximum fin surface area if there is a fixed heightavailable in the space above the printed circuit board 12.

FIG. 3B shows a heat sink 130 with fin structures 134 and 136, which arevariations of the fin structures of FIG. 3A. Heat sink 130 has a baseplate 140, with a lower portion 150 and an upper portion 152. In heatsink 130, the first fin structure 134 is above the processor 10, thesecond fin structure 136 is above the component 20, and the first finstructure 134 has a greater height H4 than heigh H5 of the second finstructure, measured from a bottom of each respective fin structure to atop 134 t, 136 t of each fin structure 134 and 136, respectively. Thetop 134 t of the first fin structure 134 attached to the lower condensersection 150 is above a top 136 t of the second fin structure 136attached to the upper condenser section 152. Using a taller finstructure 134 over the processor 10 (which generates more heat) providesgreater fin surface area for dissipating heat where it is most needed.

Referring again to FIG. 4, channels 42 may be milled into lower level 50and upper level 52 of plate 40, and run substantially the length ofplate 40, with the exception of the offset section 54 containing opening46.

Heat pipes 44 are situated within respective channels 42. Although base32 is shown as having three channels 42 with three respective heat pipes44, any number of heat pipes may be used depending on the applicationand its heat transfer requirements. Preferably, heat pipes 44 areattached to or embedded within channels 42 by epoxy adhesive bonding,but may be attached by any means known to those skilled in the artincluding brazing, soldering or the like.

Referring to FIG. 5, heat pipe 44 is an elongated tube, preferably madeof aluminum or copper, and having an s-bent shape, including lowerevaporator section 60, upper evaporator section 62, condenser section64, a wick structure (not shown), and a working fluid (not shown).Evaporator section 60 of heat pipe 44 is situated within lower level 50of plate 40 and is conductively coupled with processor 10. Evaporatorsection 62 is situated within upper level 52 of plate 40 and isconductively coupled with power supply 20. Condenser section 64 includesall of the portions of the heat pipe 44 that are remote from the heatsources, including the top and the entire offset portion betweenevaporator sections 60 and 62. Condenser section 64 includes a sectionwhich contains the s-bend between lower evaporator section 60 and upperevaporator section 62.

As is understood to those of ordinary skill in the art, heat pipe 44 isa vacuum tight tube which is evacuated and then back-filled with a smallquantity of working fluid, just enough to saturate the wick structure.The atmosphere inside the heat pipe is set by an equilibrium of liquidand vapor. The type of working fluid depends on the working temperaturerange, and may include water, methanol acetone or ammonia or the likefor microprocessor applications. The wick structure is preferably asintered powdered metal wick. Alternative wick structures include, forexample, a groove, screen, or cable/fiber wick.

Referring again to FIG. 1, the bi-level heat sink/processor/power supplyassembly 11 is assembled in the following manner. Processor fins 34 andpower supply fins 36 are attached to a top surface of base 32 bysoldering, adhesion bonding, brazing or the like. Lower level 50 andupper level 52 of plate 40 of base 32 are then mechanically attached toprocessor 10 and power supply 20, respectively, through any means knownto one of ordinary skill in the art. Base 32 of heat sink 30 may, forexample, include openings 70 for receipt of fasteners for fastening base32 to processor 10 and power supply 20. Base 32 may also includealignment pins 72 for ensuring proper alignment with these heatgenerating sources. Conductive thermal interfaces between the processor10 and plate 50, and between power supply 20 and plate 52 may be formedusing thermal grease, indium, solder, conductive epoxy, siliconadhesive, or any other conventional means.

Although the exemplary component 20 of FIG. 1 is a power supply, it iscontemplated that other component heat sources, such as co-processors,memories, or other integrated circuit packages located proximate to theprocessor 10 may be cooled using the exemplary heat sink 30. Althoughthe heat sink/multi-heat source assembly discussed above has beendescribed in terms of the heat sink thermally connected to a processorand power supply of differing heights, such a multi-level heat sinkcould be used in connection with any two heat sources of differingheights.

In the exemplary embodiments, it is advantageous to have the processor10 below the lower level 50 of the plate 40, because this allows ataller fin structure above the processor 10, which generates more heatthan power supply 20. Although the exemplary embodiment has the lowerlevel 50 of the plate 40 on processor 10 and the upper level 52 of theplate on the power supply 20, embodiments are also contemplated in whichthe lower level is on the power supply and the upper level is on thepower supply.

Although the exemplary embodiment has two levels, it is contemplatedthat heat sinks according to the invention may include three or morelevels to cool three or more components or heat sources of differingheights that are located next to each other.

Referring to FIG. 6, a bi-level heat sink 50 formed in accordance withanother embodiment of the present invention includes a processor 10, apower supply 20 and a bi-level heat sink 25. The processor and powersupply are preferably adjacent to one another and have respectivelydifferent heights, as measured from the printed circuit board 12 onwhich they are both mounted to the top of each device. The processor 10may include any type of integrated circuit package, but is preferably amicroprocessor or CPU for computer applications. A preferred applicationfor use of assembly 50 is workstations or servers employing Intel“ITANIUM™” 64-bit processors, wherein one current design includes theprocessor and the power supply situated beside each other on the board.

Referring to FIGS. 6-7, the bi-level heat sink 25 includes a bi-levelvapor chamber 100, processor fins 34 and power supply fins 36. Items inFIGS. 6 and 7 that are the same as items in FIGS. 1-5 are indicated byidentical reference numerals. Rather than having a plurality of discretetubes 44 (as in FIG. 1), heat sink 25 has a single continuous vaporchamber 100 that is nearly as wide as the plates 108 and 110. Thisunitary vapor chamber 100 provides enhanced temperature leveling acrossthe width of the plates 108 and 110.

Processor fins 34 and power supply fins 36 are preferably folded finsformed from a single sheet of metal, such as aluminum or copper.Although shown in FIG. 6 as two separate folded fins, alternatively,processor fins 34 and power supply fins 36 may be formed from a singlesheet of metal. Preferably, the folded fin has an open top design toallow natural convection with the ambient air, as well as forcedconvection. Other alternative types of fin structures may also beemployed including extruded, stamped, cold forged or machined fins, pinfins, bonded fins, or the like.

Vapor chamber 100 is a vacuum vessel including lower evaporator section102, upper evaporator section 104, condenser section 106, top plate 108,bottom plate 110, a wick structure (not shown) and a working fluid (notshown). Vapor chamber 100 preferably also includes a plurality ofinternal posts 112 which act as spacers. These internal posts 112, whichmay be solid, extend between the inside surfaces of the top plate 108and bottom plate 110. Internal posts 112 prevent the plates from bowinginward, and therefore assist in maintaining a flat surface for properthermal contact with processor 10, power supply 20 and fins 34 and 36.Alternatively, the internal posts may be porous, and may assist inproviding a capillary path for movement of condensed working fluid fromthe top (near the fins) to the bottom, which receives heat from theprocessor 10 and power supply 20. For this purpose, sintered posts maybe advantageous.

Lower evaporator section 102 is mechanically and conductively coupled toprocessor 10. Upper evaporator section 104 is mechanically andconductively coupled to power supply 20. Condenser section 106 includesthe entire top 108 of the vapor chamber, plus the portion 105 betweenevaporator sections 102 and 104. Condenser section 106 includes a lowercondenser section 107 and an upper condenser section 109. Condensersection 106 includes a section 105 which contains an s-bend betweenlower condenser section 107 and upper condenser section 109. The heightdifference between lower evaporator section 102 and upper evaporatorsection 104 of vapor chamber 100 depends on the differing heights of theprocessor 10 and power supply 20.

Top plate 108 and bottom plate 110 of vapor chamber 100 are preferablycomprised of stamped copper and are preferably sealed together with awelding process. The wick structure is preferably a copper powder wickwhich is sintered into place on inside surfaces of the top and bottomplates 108 and 110. The wick structure is preferably also present on thesurface of internal posts 112. Alternative wick structures may also beused including, groove, screen or cable/fiber. The type of working fluidwill depend on the working temperature range, but will typically includewater, methanol, acetone or ammonia for processor applications.

Referring again to FIG. 6, the bi-level heat sink assembly 50 isassembled in the following manner. Processor fins 34 and power supplyfins 36 are attached to a top surface of top plate 108 by soldering,adhesion bonding, brazing or the like to form heat sink 25. Lowerevaporator section 102 and upper evaporator section of vapor chamber 100are then mechanically attached to processor 10 and power supply 20,respectively, through any means known to one of ordinary skill in theart. Custom mechanical and attachment features can be readily designedinto heat sink 25 for attachment to the heat generating sources. Thevapor chamber 100 may be captured in a plastic or aluminum frame,allowing for a variety of mounting and alignment features that can bematched to a specific system assembly process. In addition, vaporchamber 100 and fins 34 and 36 of heat sink 25 can be manufactured withthrough-holes sized and spaced for specific applications.

Referring to FIGS. 1 and 6, the bi-level heat sink assembly 11 and 50operate in the following manner. Heat generated by the processor 10 andpower supply 20 is applied to the lower evaporator section 60 or 102 andupper evaporator section 62 or 104 of heat pipes 44 or vapor chamber 100of bi-level heat sink 30 or 25, respectively. As this heat is applied,the fluid located at these heated evaporator sections immediatelyvaporizes and the vapor rushes to fill the vacuum. The rate of fluidvaporization at each heat source will stabilize and the heat pipes 44 orvapor chamber 100 are nearly isothermal. Wherever the vapor comes intocontact with a cooler surface, such as in the condenser section 64 or106 of heat pipes 44 or vapor chamber 100, respectively, it condenses,releasing its latent heat of vaporization. The condensed working fluidreturns to the heat source via capillary action of the wick structure inthe heat pipes or vapor chamber, ready to be vaporized again and repeatthe cycle.

In the case of higher end processors which can generate in excess of onehundred watts of heat, the bi-level heat sink of the present inventionallows excess heat from the processor to be transferred and dissipatedby the fins above the power supply, a source which generatessubstantially less heat. This design efficiently utilizes the valuablespace above the power supply.

Although the invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

1-17. (canceled)
 18. A circuit board assembly, comprising: a printed circuit board including a substrate with wirings printed thereon; a processor mounted to the printed circuit board, the processor having a first height; a component mounted to the printed circuit board next to the processor, the component being a heat source, the component having a second height different from the first height; and a heat sink including a base and at least one fin structure, wherein: the base of the heat sink is continuous and has a first side abutting the component and the processor, the base has an offset between the processor and component, and the at least one fin structure is attached to a second side of the base opposite the first side wherein a first portion of said at least one fin structure has a first height and a second portion of said at least one fin structure has a second height as measured from a bottom of each respective fin within said fin structure to a top of each respective fin within said fin structure.
 19. An assembly formed with the bi-level heat sink according to claim 18 wherein a top of said fin structure located on said second side of said first base portion is coplanar with a top of said fin structure on said second base portion.
 20. The assembly of claim 18 wherein a top of said fin structure located on said second side of said first base portion is coplanar with a top of said fin structure on said second base portion.
 21. A heat sink comprising: a first base portion having a first side and a second side, said first side defining an open channel for receiving a portion of two heat pipes; a second base portion having a first side and a second side, said first side of said second base defining an open channel corresponding to said open channel in said first base portion and each receiving a corresponding portion of said two heat pipes; an offset located between said first base portion and said second base portion so that (i) said first side of said first base portion is lower than said first side of said second base portion and (ii) said second side of said first base portion is lower than said second side of said second base portion, said offset including a portion of said open channel defining an opening that exposes at least one of said two heat pipes; and a fin structure positioned upon said second side of said first base portion and said second base portion wherein a top of said fin structure located on said second side of said first base portion is substantially coplanar with a top of said fin structure on said second base portion.
 22. A heat sink comprising: a first base portion having a first side and a second side, said first side defining an open channel for receiving a portion of two heat pipes; a second base portion having a first side and a second side, said first side of said second base defining an open channel corresponding to said open channel in said first base portion and each receiving a corresponding portion of said two heat pipes; an offset located between said first base portion and said second base portion so that (i) said first side of said first base portion is lower than said first side of said second base portion and (ii) said second side of said first base portion is lower than said second side of said second base portion, said offset including a portion of said open channel defining an opening that exposes at least one of said two heat pipes; and a fin structure positioned upon said second side of said first base portion and said second base portion wherein a top of said fin structure located on said second side of said first base portion is off-set from a top of said fin structure on said second base portion. 